1. Technical Field
The present invention relates generally to internal combustion engines and, more particularly, to a misfire detection apparatus and method for detecting misfire of individual cylinders in an internal combustion engine and inhibiting misfire detection for noise related events such as a rough road condition.
2. Discussion
The Clean Air Act (1955) required motor vehicle manufacturers to reduce exhaust emissions of carbon monoxide, hydrocarbons, and oxides of nitrogen from light duty motor vehicles. To comply with the Act, most motor vehicle manufacturers generally use catalytic converters on production vehicles to control such exhaust emissions. A catalytic converter typically includes a catalyst and operates at a very high temperature in order to burn unwanted byproducts of combustion so as to reduce hydrocarbons, carbon monoxide and nitrous oxide. However, increased amounts of urnburned byproducts that often remain after the occurrence of an engine misfire can lead to damage of the catalytic converter.
More recently, regulatory agencies have proposed that passenger, light-duty and medium-duty motor vehicles with feedback fuel control systems be equipped with a malfunction indicator function that will inform the motor vehicle operator of any malfunction of an emission-related component that interfaces with an on-board computer of the motor vehicle. it is also proposed or required that an on-board diagnostic system identify the likely area of malfunction. Proposals or requirements have set forth catalyst, misfire, evaporative purge system, secondary air system, air conditioning system refrigerant, fuel system, oxygen sensor, exhaust gas recirculation, and comprehensive component monitoring requirements.
As previously mentioned, misfire of internal combustion engines can cause damage to the catalyst of a catalytic converter. With respect to misfire, the identification of the specific cylinder experiencing misfire may be required. Some regulations provide that the motor vehicle manufacturer specify a percentage of misfires out of the total number of firing events necessary for determining malfunction for: (1) the percent misfire evaluated in a fixed number of revolution increments for each engine speed and load condition which would result in catalyst damage; (2) the percent misfire evaluated in a certain number of revolution increments which would cause a durability demonstration motor vehicle to fail a Federal Test Procedure (FTP) by more than 150% of the applicable standard if the degree of misfire were present from the beginning of the test; and (3) the degree of misfire evaluated in a certain number of revolution increments which would cause a durability demonstration motor vehicle to fail an inspection and maintenance (IM) program tailpipe exhaust emission test.
Current and proposed future regulations are also requiring that motor vehicle manufacturers be able to provide information detailing the occurrence of misfires such as identifying which cylinders are responsible for one or more misfires. The misfire information need be collected and stored in memory so that the stored information may be downloaded at a service center and used to determine the cause of misfires in the vehicle. One misfire detection and identification approach is disclosed in issued U.S. Pat. No. 5,361,629 issued Nov. 8, 1994 and titled "Single Sensor Misfire Detection Apparatus and Method for an Internal Combustion Engine". The above-cited patent is also hereby incorporated by reference. The misfire detection approach in the above-cited patent senses rotation of a crankshaft and calculates a crankshaft velocity based on the sensed rotation. The calculated crankshaft velocity changes or a compensated velocity change is compared to a predetermined crankshaft velocity range to determine if misfire occurred.
Despite the advances made in engine misfire detection, many of the conventional approaches still suffer some problems. First, some approaches are susceptible to detecting a false misfire which really is a disturbance caused by a previous misfire. Secondly, some approaches can be tricked into falsely identifying noise, which can be generated by drive line disturbance, as a misfire. This noise condition is commonly referred to as a "rough road" condition. Such problems exist in the prior art due in part to the assumption that misfire causes only negative acceleration values and that any positive values must solely be attributed to noise. While this is often true, there are a number of exceptions. For example, low engine speed and low frequency misfires can cause large torsional vibrations that would signal a false rough road condition. Also, certain high frequency misfires, such as the situation with a four-cylinder engine and a distributorless ignition system (DIS) where multiple cylinders share a common coil, removal of one spark plug wire may also cause a large positive change in velocity.
It is therefore one object of the present invention to provide for an improved apparatus and method of detecting cylinder misfires in an internal combustion engine.
It is another object of the present invention to provide for a misfire detection apparatus and method which is less susceptible to provide a false misfire detection caused by rough road conditions or other noise-related events.
More particularly, it is an object of the present invention to provide for a misfire detection apparatus and method which is capable of detecting misfire events and distinguishing actual misfire from noise-related events such as a rough road condition.
It is yet a further object of the present invention to provide for such a misfire detection apparatus and method which disables misfire detection upon detection of a rough road condition.